5V Line on PC Power Supply

[whynotpizza]

Can I use a single 5V power line (yellow, black, red) from a standard PC power supply to drive ~35 LED lights in a simple ON/OFF configuration with 1 switch?

It is right to assume ~15miliamps from each LED for a total of ~550milliamps?

That amount of current should work with a standard PC 5V power rail, right?

(I would obviously use the RED and BLACK for 5V rail)

[MonMotha]

While it varies highly with the era of the supply, figure you can get at least 15A off the 5V rail of a PC supply.  Wire to the "hard drive" connectors is usually AWG18 which, over that short distance, can handle 5A or so.  550mA is decidedly not a problem.

[BobA]

Please remember that the +5v is red and the GND is black.   If you use a tap such as for a fan will have a red wire but close inspection will see that it is connected to the 12V yellow wire so do not use a fan power tap.

[Louis Tully]

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[whynotpizza]

Excellent, thanks.

Do you think 22gauge wire (single stand for Ground and multi-strand for Power) is enough to handle this small amount of current?

Thanks again for the help!

  David

[PL1]

Do you think 22gauge wire (single stand for Ground and multi-strand for Power) is enough to handle this small amount of current?

This table indicates that 22AWG should be good for power transmission up to 0.92 Amps.


Scott

[lilshawn]

i wouldn't push 22ga far or high...and i'll tell you why...

a weird thing happens with small wire gauge, you end up with "loss" in the wire, this is because the diameter of the conductor is small. It's only a couple of milliohms, but the wire itself has a little bit of resistance. this problem gets worse as the current it carries gets bigger... This is because the wire can actually heat up making this problem even worse in several orders of magnitude. (as temperature increases so does resistance.)

22 ga wire has 16 ohms of resistance over 1000ft (ideally, and of course NOTHING is ideal) so a foot has .016 ohms which isn't much, but you start throwing high current and high temps at that wire, it's likely to get pretty high. Don't forget you'll need to double that because you have 1 wire for positive and another for the neg.

in conclusion, if you are going a short distance (maybe less than 1 or 2 feet) it's probably fine, if you have 6 feet to get there, I'd choose something bigger or move your power supply closer to where you need.

I would also stick to stranded not solid wire. if you flex solid, it has a chance of breaking. I guess if it's all you got and the wire will never move go for it.

Don't be afraid to splurge on a few rolls wire, it's cheap and it never goes bad. it never hurts to have extra laying around, you never know when you need an extra clothesline or need to hang up some parts to paint.

[MonMotha]

550mA (about half an amp) on AWG22 is probably fine over a few feet, but in general I like to use no smaller than AWG18 for power transmission in appliances.  The reason has just as much to do with mechanical strength as it does electrical issues.  A lot of people use AWG20 for this, but I prefer to only stock #22 and #18.